Axial air gap motors have been employed for many years. During that time they have taken many configurations. The motors use magnets in combination with rotating, flat profile windings made either from stampings, etchings or conventionally wound wire that have been employed for some time in DC and AC motors.
Axial air gap motors are often referred to as flat or "pancake" motors, and have been employed in numerous applications where length is an important design consideration. In general, axial air gap armature designs provide the shortest length motor profiles currently available. The motors are characterized by axial air gap, printed, stamped or wire wound armatures. The motors are also characterized by axially or radially oriented brush/spring assemblies for axial or radial commutation.
While axial air gap motors have proven themselves beneficial for their desired purposes, today there are many applications where reduction of length must be optimized even further. For example, this is the case with motors used in many automotive applications, such as in radiator and condenser cooling modules, as well as window lifts, blower assemblies and the like. Engine compartments and body panels in automobiles are constantly decreasing in available volume, while passenger space is constant or increasing. Consequently, minimizing length and weight, as well as costs, while maximizing power output are important criteria for not only automotive applications but also other applications of "pancake" motors, as, for example, aerospace, industrial and other commercial applications.
A typical prior art air gap motor is shown in FIG. 1. Permanent magnets 10 are fixedly secured to endplates 12 of the stator. The endplates are made of magnetic, permeable materials (for example, steel or iron) and act as a flux return path. The housing 14 is completed by an aluminum cylindrical outer ring 16 positioned between the endplates 12. An armature 18 mounted on a rotary shaft 20 is provided in the space between the magnets 10. Current is applied to the armature 14 through brushes 22. The armature 18 is a conventional profile winding made either from stampings, etchings or conventional wound wire.
Currently, axial air gap motors, such as the one disclosed in FIG. 1, are constructed with a stator assembly consisting of a set of permanent magnets 10 on one or both sides of the armature 18. The magnets 10, are typically bonded to endplates 12 of magnetic, permeable material, for example, cold rolled steel or iron. The magnets are most commonly made of Alnico material, although in recent years motors with high coercivity magnets containing rare earth elements (samarium cobalt, neodymium, or praesydmium) have become available. The prior art motor further includes a wave washer 24 and a charge coil winding 26.
The armatures of axial air gap motors are usually stampings, etchings or conventional wire windings. The following U.S. patents are exemplary of armature designs currently utilized:
U.S. Pat. No. 3,488,539 ("Tucker") PA1 U.S. Pat. No. 3,575,624 ("Keogh") PA1 U.S. Pat. No. 3,737,697 ("Kitamori et al.") PA1 U.S. Pat. No. 4,321,499 ("Gupta") PA1 U.S. Pat. No. 4,341,973 ("Maruko et al.") PA1 U.S. Pat. No. 4,413,895 ("Lee") PA1 U.S. Pat. No. 4,794,293 ("Fukisaki et al.") PA1 U.S. Pat. No. 5,099,162 ("Sawada") PA1 U.S. Pat. No. 5,144,183 ("Farrenkopf").
As stated previously, prior axial air gap motors use the motor endplates as a flux return path. As a result, the endplates must be made from expensive materials, such as steel or iron, which must be plated to prevent oxidation. Although lighter weight and less costly material, such as aluminum, would facilitate significant savings, aluminum endplates cannot be used in present motors since aluminum does not have the necessary permeability to be used as a flux return path.
Additionally, stators (that is, magnets, endplates and brushes) of prior art motors require a long assembly time since they are made from a "series" build. That is, each step of the assembly process is contingent upon, and cannot be started before, the prior assembly is completed. As a result, magnets cannot be bonded to the endplates until the endplates are made, brushes and bearings cannot be inserted until the magnets are bonded, etc. This lengthens the manufacturing cycle, tends to increase inventory, and seriously impedes a manufacturer's ability to increase responsiveness to customers.
The use of Alnico magnets in prior art motors requires that the magnet charging be done in situ. As such, an internal charge wire must be built into, and remain, in the motor. However, the recent use of high coercivity magnets containing rare earth elements in axial air gap motors has eliminated this problem. Despite these advances, designs for axial air gap motors have not fully utilized the cost benefits these high coercivity magnets facilitate.
Additionally, modifying motor performance characteristics (that is, increasing torque and/or power) in existing axial air gap motors is typically difficult and requires significant redesign. Specifically, torque can only be increased by either increasing the material grade, decreasing the air gap, or increasing the magnet dimensions (typically length). In doing so, significant design costs are incurred, a propagation of new parts occur that must be introduced, maintained, and warehoused, the difficulty of maintaining the motor increases and inventory costs increase. In addition, motor length must typically increase to accommodate the longer magnets required by higher torque motors. The increase in motor length tends to nullify the advantages associated with the flat profiles provided by axial air gap motors.
Finally, current axial air gap motors are difficult to manufacture, require significant assembly, tooling and jigs, require significant assembler training, and have long manufacturing cycle times and high inventory costs.
Despite the advances made by presently available axial air gap motors, it is apparent that the need for a convenient, inexpensive and reliable motor still remains. The present invention fulfills this need.